You're in the grocery store shopping for a carton of orange juice for tomorrow's breakfast and you're faced with a decision — plain old juice or, for no extra cost, one fortified with bone-building calcium.

Rates of women who are opting for preventive mastectomies, such as Angeline Jolie, have increased by an estimated 50 percent in recent years, experts say. But many doctors are puzzled because the operation doesn't carry a 100 percent guarantee, it's major surgery -- and women have other options, from a once-a-day pill to careful monitoring.

"There's a finite volume in the stomach and everybody is vying for that volume," says Fergus Clydesdale, distinguished professor and department head at the University of Massachusetts, Amherst. "One way to try to get a part of the share of that volume is to offer something that has some health benefit."

The term "functional food" has no legal definition. While it has long referred to fare beneficial to a person's health, such as broccoli, it's increasingly used to refer to designer foods or ones that have been modified to incorporate nutrients they wouldn't normally contain for a specific health purpose. A box of pasta with heart-healthy omega-3 fatty acids — normally found in fish — is a prime example.

And consumers, who are swimming in information about the relationships between foods or their ingredients and disease risks, are eating them up.

Three-quarters of consumers said they're trying to eat more fiber and whole grains, and half said they're trying to get more omega-3 fatty acids, according to an online International Food Information Council Foundation survey of 1,000 Americans 18 and older in late 2005. About 83 percent of respondents said they're interested in learning more about foods that offer health benefits beyond basic nutrition.

Women with children and the growing baby boomer population are most into these foods, says Wendy Reinhardt Kapsak, the foundation's director of health and nutrition, due to their focus on overall wellness and disease prevention.

People disenchanted with the medical system are also looking for more ways to control their destiny, says Clydesdale. They're using food to do it.

The trend is not entirely new. Manufacturers have been fortifying milk with vitamin D since the 1930s to prevent rickets, a disease caused by a vitamin D deficiency and characterized by defective bone growth in children. Since the vitamin isn't naturally found in a lot of foods, it can be difficult for people who are lactose intolerant, or simply don't like milk, to consume healthy amounts. Today, thanks to modern technology, you can drink a glass of orange juice packed with vitamin D for the same effect.

Worth it?The question is: How much of these extra benefits do you need? You can get too much of a good thing without realizing it, says registered dietitian Cynthia Sass, a spokeswoman for the American Dietetic Association.

"The idea of a supplement or fortified foods is to fill a gap, to bring a person up to the recommended intake," she says. "If you're already at the recommended intake, it's not going to do anything for you. It may work against you."

For instance, exceeding the tolerable upper intake level for vitamin C, 2,000 miligrams a day for adults, can cause diarrhea, an upset stomach and kidney stones. Likewise, while plant sterols and stanols added to your granola bar may help lower your cholesterol, you need only two grams of the substances a day. Exceeding that amount won't give you any extra benefit and the long-term effects of getting too much are unknown, according to medical research in the Harvard Heart Letter.

Then again, you may be buying a product promising benefits you're not getting.

Beverages containing herbs often don't state how much echinacea or ginseng, for instance, they actually contain. And universities and medical centers rarely take two groups of people, give one a certain food and withhold from the other to see the difference in outcomes, Sass says.

Iron might be added to your food, but in some forms it's insoluble and the body will flush it out without getting anything from it, Clydesdale says. You have to question whether the additive is able to be absorbed by your body.

That said, if a product makes a health claim, e.g., "calcium may reduce the risk of osteoporosis," there has to be science behind it to get the Food and Drug Administration's approval.

An eye on caloriesBut that may not make a trip to the grocery store any less confusing.

While Sass thinks it's great that consumers are getting the link between nutrition and health, she suggests people keep in mind the USDA's research-based dietary guidelines when considering changing the way they eat.

"I'm more for getting (nutrients) from the original source if you can," she adds.

Of course, not everyone buying these foods and beverages is purposely seeking out a health benefit.

When 3 p.m. rolls around on any given weekday, people tend to feel tired and a little hungry. They may turn to coffee, tea or an energy drink for that boost, says Steve Haley, CEO and president of Celsius Holdings, which offers green tea-enhanced Celsius — "the earth's first calorie-burning soda." In 2006, the company saw more than $1.5 million in revenue and expects to blow past the figure this year.

Haley notes that if we all ate balanced diets, exercised regularly, drank plenty of water and got enough sleep, we wouldn't need these kinds of products. But since nobody's perfect, maybe some extra fortification isn't a bad thing.

While a small clinical research study presented at the 2005 International Society of Sports Nutrition conference supports Celsius' claim that the soda raises the metabolism for up to three hours after consumption, the company doesn't make weight-loss claims or promote it as an alternative to exercise. Instead, it encourages people to drink the product as part of a healthier lifestyle, a point nutrition experts echo.

"What consumers need to be wary of with all of these healthy, functional foods out there is that they still need to keep an eye on calories, especially with the obesity and overweight problems we have," says Lori Hoolihan, registered dietitian and nutrition research specialist with the Dairy Council of California's Functional Food Task Force.

"Don't assume you can have as much as you want," she says, "because it's considered healthy."